Magnetic recording medium

ABSTRACT

A magnetic recording medium comprises a magnetic alloy layer on a substrate wherein said magnetic alloy layer is made of 70-90 wt. % of Co and 30-10 wt. % of at least one of Si, Sb, Li, V, Ta, Ge and Pt and a magnetization axis of said magnetic alloy is substantially vertical to said layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vertical type magnetic recordingmedium.

2. Description of the Prior Art

A vertical type magnetic recording medium has been proposed as a newrecording system for super dense recording (Japanese Unexamined PatentPublication No. 134706/1977).

The magnetic medium used for this purpose must have high magneticanisotropy in vertical direction on the layer and high coercive force.It has been disclosed that a Co--Cr layer prepared by a high frequencysputtering process is excellent medium suitable for the aforementionedcondition.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a vertical typemagnetic recording medium which has magnetic characteristics superior tothe magnetic recording medium having a Co--Cr layer.

The foregoing and other objects of the present invention have beenattained by providing a magnetic recording medium which comprises amagentic alloy layer on a substrate wherein said magnetic alloy layer ismade of 70-90 wt.% of Co and 30-10 wt.% of at least one of Si, Sb, Li,V, Ta, Ge and Pt and a magnetization axis of said magnetic alloy issubstantially vertical to said layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The vertical type magnetic recording medium having a magnetic alloylayer made of 70-90 wt.% of Co and 30-10 wt.% of at least one of Si, Sb,Li, V, Ta, Ge and Pt has excellent magnetic characteristics.

The condition required for the vertical type magnetic recording mediumis to give a high crystalline orientation in perpendicular to the layer,high anisotropy and high coercive force so as to give easy verticalmagnetization.

In accordance with the present invention, these characteristics aregiven by using a magnetic alloy layer made of Co and the other metalcomponent of Si, Sb, Li, V, Ta Ge or Pt thereby providing a magneticrecording medium having the magnetic characteristics superior to thoseof the Co--Cr alloy layer.

The reason why the magnetic recording medium of the present inventionhas excellent magnetic characteristics is not clearly understood.According to many tests for various metals and metalloids which aresolid-soluble into Co, the additional component combined with Coimproves a thermal stability of a vertical crystalline orientation of Co(A half-value width Δθ₅₀ of a rocking curve in hcp (002) reflection ofCo in an X-ray diffraction is an index of the orientation). That is thethermally stable region having hcp structure of Co is enlarged by thecombination of the metal or metalloid as the additional component.

With regard to the content of Co, when the content of Co is less than 70wt.%, a ferromagnetism is too low whereas when it is more than 90 wt.%,the basic characteristic required for the vertical type magnetic layerH_(k) <4πM_(s) is not satisfied. Therefore, it is not suitable to use itas the vertical type magnetic recording medium.

A content of Co is preferably in a range of 77 to 88 wt.% especiallyabout 80% to impart the optimum magnetic characteristics.

A thickness of the layer is selected from the range of 500 Å to 3 μm.When it is thinner than 500 Å, the magnetic moment is too low and asatisfactory S/N ratio is not given in the form of the magneticrecording medium whereas when it is more than 3 μm, the improvement ofthe characteristics corresponding to the increase of the cost is notfound.

When the combination of Co--Si, Co--Li, Co--Si-other component orCo--Li-other component is employed for the magnetic layer, the optimummagnetic characteristics are given.

The present invention will be illustrated by certain examples andreferences which are provided for purposes of illustration only and arenot intended to be limiting the invention.

EXAMPLE

Each thin layer made of each binary alloy of 80 wt.% of Co and 20 wt.%of each additional component of Si, Sb, Li, V, Ta, Ge or Pt and eachternary alloy of 80 wt.% of Co, 10 wt.% of Li and 10 wt.% of V; or 80wt.% of Co, 10 wt.% of Si and 10 wt.% of Sb was formed on a film by ahigh frequency sputtering process. The condition of the sputteringprocess is shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Substrate            Polyimide film                                           ______________________________________                                        Background gas pressure                                                                            4.9 × 10.sup.-7 Torr                               Argon gas pressure   1.0 × 10.sup.-2 Torr                               High frequency electric                                                                            300 W                                                    power                                                                         Temperature of substrate                                                                           180° C.                                           Thickness of layer   0.5 μm                                                ______________________________________                                    

Each crystalline orientation (half-value width Δθ₅₀ of rocking curve ofhcp (002) reflection of Co by X-ray diffraction); each anisotropicmagnetic field H_(k) ; and each coercive force in vertical directionH_(c) (⊥) of each layer were measured. The results are shown in Table 2.

The results show the following fact. The Co type alloy layers of thepresent invention impart sharp crystalline orientation high anisotropicmagnetic field and high coercive force in vertical direction and areremarkably suitable for a vertical type magnetic recording medium.

The inventors have investigated almost all metals and metalloids whichare solid-solubilizable with Co. As a result, the components of thepresent invention give superior magnetic characteristics.

The content of Co was changed in the similar experiments. When thecontent of Co is less than 70 wt.%, ferromagnetism is lowered whereaswhen it is more than 90 wt.%, the condition of H_(k) >4πM_(s) is notgiven whereby they are not suitable for the vertical type magneticrecording medium.

It has been found that the content of Co is preferably in a range of77-88 wt.% especially about 80 wt.%.

When a thickness of the layer is less than 500 Å, the magnetic moment istoo low whereby a desired S/N ratio is not given in the application asthe magnetic recording medium. When the thickness is more than 3 μm, theimprovement of the characteristics corresponding to the increase of thecost is not found.

                  TABLE 2                                                         ______________________________________                                        Crystalline orientation and magnetic characteristics                          Alloy     Δθ.sub.50 [°]                                                          H.sub.k [KO.sub.e ]                                                                    H.sub.c (⊥)[KO.sub.e ]                    ______________________________________                                        Co--Cr    2.8         6.00     1.20                                           (reference)                                                                   Co--Si    2.5         6.38     1.40                                           Co--Sb    2.6         6.05     1.20                                           Co--Li    2.5         6.38     1.40                                           Co--V     2.7         6.05     1.23                                           Co--Ta    2.7         6.05     1.29                                           Co--Ge    2.6         6.20     1.28                                           Co--Pt    2.6         6.20     1.31                                           Co--Li--V 2.4         6.42     1.42                                           Co--Si--Sb                                                                              2.3         6.32     1.39                                           ______________________________________                                    

We claim:
 1. A magnetic recording medium which comprises a magneticalloy layer on a substrate wherein said magnetic alloy layer is made of70-90 wt.% of Co and 30-10 wt.% of at least one of Si, Sb, Li, V, Ta, Geand Pt and a magnetization axis of said magnetic alloy is substantiallyvertical to said layer.
 2. The magnetic recording medium according toclaim 1 wherein said magnetic alloy layer has a thickness of 500 Å to 3μm.